1. Field of the Invention
This invention pertains to venetian blinds employing a window-mounted headrail, a series of horizontal blind slats and bottom rail with an arrangement of lift cords passing through slat apertures to raise and lower the slats and bottom rail and to retain the slats in a vertically stacked relationship regardless of the position of the blind with respect to the window. More particularly, the invention is directed to an improvement of the apertures in the slats through which the lift cords pass, specifically to the shape and relative size of the apertures resulting in the reduction of light passing through the assemblage of blind slats.
2. Material Art
The related application is directed to the positioning of slat apertures immediately adjacent to the slat ends and also discloses a typical prior art blind where the slat apertures are well inboard of the slat ends at the same lateral position as the tilt ladders normally associated with a venetian blind. In both cases, the slat apertures, sometimes referred to as "rout holes" are typically rectangular in shape and extend medially of the slats over about one-half of the slat width. The corners of the ends of the rectangular slot may be rounded. Illustrative of the rectangular slots, apertures or rout holes is U.S. Pat. No. 4,739,816 (FIG. 8) and a myriad of commercial venetian blinds seen in the marketplace.
Since the primary function of a venetian blind is to provide light control, it is desirable that the blind allow as little light seepage as possible, not only by means of orienting the angle of the slats to the light (typically by use of tilt ladders and tilt control mechanisms in the headrail operable by a tilt wand), which is controllable feature of a blind, but also between the ends of the slats and the window mullions, the head channel and the slats, and the bottom rail and the window sill.
Light seepage also occurs at the point of the rout holes. In the past, there have been many attempts to reduce the size of the apertures so as to reduce light passage. However, since the rout holes must provide free and unencumbered passage of the lift cords through the slats, regardless of the slat's angle of tilt, the rout holes are typically rectangular in shape, and have a uniform opening sufficiently wide for the lift cord's passage.
FIG. 3 hereof illustrates a typical prior art rout hole which in a nominal one inch (2.46 cm.) wide slat has a longitudinal length l of about 1.10 cm. and a width w of about 0.30 cm. with an open area A of about 0.312 cm.sup.2. It is medially spaced a distance d of about 0.79 cm from each of the edges of the slat.
A typical woven nylon or polyester lift cord 14 of 0.127 cm. is employed, as illustrated, which blocks out light particularly in the slat-tilted-closed position but still leaves an area B on both sides of the cord 14 parallel to the rout hole parallel edges 50 of approximately 0.185 cm.sup.2. These relatively wide areas in each vertical row (typically two or three in number) of the series of slats results in a high degree of light penetration through each of the areas B. The width of the prior art rout holes relative to the diameter of the lift cord also results in considerable lateral movement of the slats causing a degree of misalignment of the edges of the series of slats. Further, due to the size of the prior art rout holes and the need to retain structural rigidity and strength at the slat-weakening rout hole, a relatively high slat material gage thickness has been required. Typically in a 2.46 cm wide aluminum slat a gage thickness of about 0.017 cm has been employed.
Typically, as a hole is punched in precoated (painted) slat material, the walls of the punched holes are left as a bare, uncoated surface. The greater the material gage and the larger the rout hole, the more apparent the unfinished edge. This situation is magnified when the hole is punched in darker colored material. In an assembled blind, the uncoated surface reflect light and accent the vertical lines caused by the rout holes.